In continuation of our previous studies, photoaffinity and fluorescent derivatives of streptomycin and several other aminoglycoside antibiotics are in preparation for use as probes in the investigation of several problems concerned with the action of these antibiotics: 1) the nature and site of their ribosomal binding to E. coli ribosomes; 2) their use to identify and determine the kinetic distribution of the intermediates which accumulate during intracellular blockade of protein synthesis by these antibiotics; 3) the kinetics of ribosomal assembly; 4) their use to study intracellular antibiotic transport and some problems related to the mechanism of this process. (NOTE: The title of this project has been changed in the present renewal request over that previously in effect, in order to more accurately reflect the current direction taken. The previous title was "Metabolism of Normal and Bacteriophage-infected E. coli".)